cosmetic dermatology - prins and pract. 2nd ed - l. baumann, et al., (mcgraw - hill, 2009)

Cosmetic
Dermatology
PRINCIPLES AND PRACTICE
SECOND EDITION
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Cosmetic
Dermatology
PRINCIPLES AND PRACTICE
SECOND EDITION
LESLIE BAUMANN, MD
Author and Editor
Director, University of Miami
Cosmetic Medicine and Research Institute
Professor of Dermatology
University of Miami
Miami Beach, FL

SOGOL SAGHARI, MD
Associate Editor
Department of Dermatology
University of Miami
Miami, FL
Private Practice
Los Angeles, CA
EDMUND WEISBERG, MS
Managing Editor
Center for Clinical Epidemiology and Biostatistics
University of Pennsylvania School of Medicine
Philadelphia, PA
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Dedication
This book is dedicated to the three men in my life:
Roger Alexander Baumann
Thank you for encouraging me and being there to help
me with all the technology and business aspects of my
life. Your never- ending support has kept me sane over
the years. Most of all, my thanks for dragging me out of
the mud when times were tough like a good cutting
horse does! You are an ideal husband, father, and friend.
Here’s to another 20 years together!
Robert Edward Baumann
I am so proud of what a good person you are growing up
to be. You are kind, have a great sense of humor, and
have a love for others that is truly refreshing. You have
many talents, one of which is making me feel very special
and proud to have you as a son.
Keep up the good work!
Maximilian Carl Baumann

When this book comes out, you will be 7 years old. It is
hard to believe that you are growing up so fast; however,
you will always be my baby. I am very proud of what a
great student and person you are. I am so happy to have
someone in the family who is so much like me and loves
to read as much as I do.
Never stop snuggling!
Roger, Robert and Max,
You all brighten my life, remind me of what is important,
and make it all worthwhile.
Thank you for loving me!
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vii
CONTENTS
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii
Section 1. Basic Concepts of Skin Science
1 Basic Science of the Epidermis . . . . . . . . . . . . . . . . . . . 3
Leslie Baumann and Sogol Saghari
2 Basic Science of the Dermis . . . . . . . . . . . . . . . . . . . . . . 8
Leslie Baumann and Sogol Saghari
3 Fat and the Subcutaneous Layer . . . . . . . . . . . . . . . . 14
Voraphol Vejjabhinanta, Leslie Baumann, Suzan
Obagi, and Anita Singh
4 Immunology of the Skin . . . . . . . . . . . . . . . . . . . . . . . . 22
H. Ray Jalian and Jenny Kim
5 Hormones and Aging Skin . . . . . . . . . . . . . . . . . . . . . . 29
Larissa Zaulyanov-Scanlan
6 Photoaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Leslie Baumann and Sogol Saghari
7 Cigarettes and Aging Skin . . . . . . . . . . . . . . . . . . . . . . 42
Leslie Baumann and Sogol Saghari
8 Nutrition and the Skin . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Leslie Baumann
Section 2. Skin Types
9 The Baumann Skin Typing System . . . . . . . . . . . . . 69
Leslie Baumann and Edmund Weisberg
10 Oily Skin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Mohamed L. Elsaie and Leslie Baumann
11 Dry Skin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Leslie Baumann
12 Sensitive Skin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Leslie Baumann
13 Skin Pigmentation and Pigmentation
Disorders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Leslie Baumann and Sogol Saghari
14 Skin of Color . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Heather Woolery-Lloyd
Section 3. Specific Skin Problems
15 Acne (Type 1 Sensitive Skin) . . . . . . . . . . . . . . . . . . 121
Leslie Baumann and Jonette Keri
16 Rosacea (Type 2 Sensitive Skin) . . . . . . . . . . . . . . . 128
Sogol Saghari, Jonette Keri, Stuart Shanler and Leslie Baumann
17 Burning and Stinging Skin (Type 3
Sensitive Skin) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
Leslie Baumann
18 Contact Dermatitis (Type 4 Sensitive Skin) . . .136
Sharon E. Jacob
19 Wrinkled Skin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

Sogol Saghari and Leslie Baumann
20 Chemical Peels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
Leslie Baumann and Sogol Saghari
21 Prevention and Treatment of Bruising . . . . . . . . . 163
Susan Schaffer, Sogol Saghari and Leslie Baumann
Section 4. Cosmetic Procedures
22 Botulinum Toxin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
Leslie Baumann, Mohamed L. Elsaie and Lisa Grunebaum
23 Dermal Fillers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
Leslie Baumann, Marianna Blyumin and Sogol Saghari
24 Lasers and Light Devices . . . . . . . . . . . . . . . . . . . . . . 212
Joely Kaufman
25 Sclerotherapy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
Larissa Zaulyanov-Scanlan
CONTENTS
viii
26 Facial Scar Revision . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
Suzan Obagi and Angela S. Casey
Section 5. Skin Care
27 Starting a Skin Care Product Line . . . . . . . . . . . . . . 237
Leslie Baumann
28 Cosmetic and Drug Regulation . . . . . . . . . . . . . . . . 241
Edmund Weisberg and Leslie Baumann
29 Sunscreens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
Leslie Baumann, Nidhi Avashia and
Mari Paz Castanedo-Tardan
30 Retinoids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
Leslie Baumann and Sogol Saghari
31 Cleansing Agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
Kumar Subramanyan and K.P. Ananth

32 Moisturizing Agents . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
Leslie Baumann
33 Depigmenting Agents . . . . . . . . . . . . . . . . . . . . . . . . . 279
Leslie Baumann and Inja Bogdan Allemann
34 Antioxidants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292
Leslie Baumann and Inja Bogdan Allemann
35 Anti-inflammatory Agents . . . . . . . . . . . . . . . . . . . . . 312
Mari Paz Castanedo-Tardan and Leslie Baumann
36 Fragrance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325
Edmund Weisberg and Leslie Baumann
37 Preservatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329
Edmund Weisberg and Leslie Baumann
Section 6. Other
38 Bioengineering of the Skin . . . . . . . . . . . . . . . . . . . . 335
Leslie Baumann and Mari Paz Castanedo-Tardan
39 Scales Used to Classify Skin . . . . . . . . . . . . . . . . . . . 342
Mari Paz Castanedo-Tardan and Leslie Baumann
40 The Psychosocial Aspects of Cosmetic
Dermatology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
Edmund Weisberg
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357
CONTENTS
ix
Inja Bogdan Allemann, MD
Cosmetic Dermatology Fellow,
Department of Dermatology and
Cutaneous Surgery, Miller School
of Medicine, University of Miami,
Miami, Florida; Dermatologic
Clinic, University Hospital of

Zurich
Zurich, Switzerland
Chapters 33 and 34
K. P. Ananth
Chapter 31
Nidhi J. Avashia, BS
Miller School of Medicine, University
of Miami, Miami, Florida
Chapter 29
Marianna L. Blyumin, MD
Dermatology Resident, Department of
Dermatology and Cutaneous
Surgery, Miller School of Medicine,
University of Miami, Miami,
Florida
Chapter 23
Angela S. Casey, MD
Assistant Professor, Dermatology and
Mohs Surgery, University of Vermont
College of Medicine, Fletcher Allen
Health Care, Burlington, Vermont
Chapter 26
Maria Paz Castanedo-Tardan, MD
Department of Dermatology and
Cutaneous Surgery, Miller School of
Medicine, University of Miami
Miami, Florida
Chapters 29, 35, 38, and 39
Mohamed L. Elsaie, MD, MBA
Cosmetic Dermatology Fellow,

Department of Dermatology and
Cutaneous Surgery, Miller School of
Medicine, University of Miami, Miami,
Florida; Department of Dermatology
and Venereology, National Research
Center, Cairo, Egypt
Chapters 10 and 22
Lisa Danielle Grunebaum, MD
Assistant Professor, Division of Facial
Plastic and Reconstructive Surgery,
Department of Otolaryngology and
Head and Neck Surgery, University
of Miami, Miami, Florida
Chapter 22
Sharon E. Jacob, MD
Assistant Professor, Divisions of
Medicine and Pediatrics
(Dermatology), University of
California, San Diego, San Diego,
California
Chapter 18
H. Ray Jalian, MD
Resident Physician, Department of
Medicine, Division of Dermatology,
David Geffen School of Medicine at
UCLA, Los Angeles, California
Chapter 4
Joely Kaufman, MD
Assistant Professor, Department of
Dermatology and Cutaneous Surgery

and Director of Laser and Light
Therapy, University of Miamia
Cosmetic Medicine and Research
Institute, Miami, Florida
Chapter 24
Jonette Keri, MD, PhD
Assistant Professor, Miller School of
Medicine, University of Miami,
Miami, Florida;
Chief, Dermatology Service, Miami VA
Hospital, Miami, Florida
Chapters 15 and 16
Jenny Kim, MD, PhD
Associate Professor, Department of
Medicine and Division of
Dermatology, David Geffen School
of Medicine at UCLA, Los Angeles,
California
Chapter 4
Suzan Obagi, MD
Assistant Professor of Dermatology,
Director, The Cosmetic Surgery and
Skin Health Center, University of
Pittsburgh Medical Center,
Pittsburgh, Pennsylvania
Chapters 3 and 26
Sogol Saghari, MD
Department of Dermatology,
University of Miami, Miami, Florida;
Private Practice, Los Angeles,

California
Chapters 1, 2, 7, 13, 16, 19, 20, 21, 23,
and 30
Susan Schaffer, RN
University of Miami, Cosmetic
Medicine and Research Institute,
Miami Beach, Florida
Chapter 21
Stuart Daniel Shanler, MD, FACMS
Private Practice, New York, New York
Chapter 16
CONTRIBUTORS
CONTRIBUTORS
x
Anita Singh, MS
Miller School of Medicine, University
of Miami, Miami, Florida
Chapter 3
Kumar Subramanyan, PhD
Senior Manager, Consumer and Clinical
Evaluation, Unilever Global Skin
Research & Development
Shanghai, China
Chapter 31
Voraphol Vejjabhinanta, MD
Postdoctoral Fellow, Mohs, Laser and,
Dermatologic Surgery, Department of
Dermatology and Cutaneous Surgery,
Miller School of Medicine,University
of Miami, Miami, Florida; Clinical

Instructor
Suphannahong Dermatology Institute,
Bangkok, Thailand
Chapter 3
Edmund Weisberg, MS
Managing Editor, Center for Clinical
Epidemiology and Biostatistics,
University of Pennsylvania School of
Medicine, Philadelphia, Pennsylvania
Chapters 9, 28, 36, 37, and 40
Heather Woolery-Lloyd, MD
Assistant Professor, Department of
Dermatology and Cutaneous Surgery,
Director of Ethnic Skin Care
University of Miami Cosmetic
Medicine and Research Institute,
Miami, Florida
Chapter 14
Larissa Zaulyanov-Scanlan, MD
Voluntary Faculty, University of Miami
Cosmetic Medicine and Research
Institute, Miami Beach, Florida;
Private Practice, Delray Beach, Florida
Chapters 5 and 25
CONTRIBUTORS
xi
Cosmetic dermatology is a rapidly grow-
ing field that can attribute its popularity
to aging baby boomers. Although many
dermatologists perform cosmetic proce-

dures and millions of dollars are spent
each year on cosmetic products, there is a
paucity of published research in this field.
I was stimulated to write this text
because I have found it challenging to
conduct thorough research in preparation
for my lectures and articles on cosmetic
science as there exists no undisputed ref-
erence at the moment. Of the research
performed by cosmetic scientists, much
of it, unfortunately, is proprietary infor-
mation owned by corporations and is not
published or shared in any way for the
immediate benefit of the medical com-
munity and other cosmetic professionals.
This results in each company or cosmetic
scientist having to “reinvent the wheel.”
My goal, with this book, is to create a
link, featuring a better streaming flow of
information, between the fields of der-
matology and cosmetic science. This text
is designed to help cosmetic dermatolo-
gists understand the available informa-
tion on various cosmetic products and
procedures. It should also help cosmetic
chemists to understand the issues that
cosmetic dermatologists deal with on a
frequent basis. In addition, this text
should fill the gap in knowledge among
professionals such as aestheticians who

need to know what to apply to patients’
or clients’ skin and about the products
that people purchase over-the-counter
and apply to their skin. This text should
help these professionals answer the ques-
tions that their clients/patients ask about
skin care products and their scientific
validity. It is my hope that this text will
encourage cosmetic dermatologists, cos-
metic scientists and aestheticians to insist
upon well researched cosmetic products
and procedures. By working together in
this way we can preserve the integrity of
an exciting and rapidly developing field
of study.
Research in the field of cosmetic der-
matology should be encouraged for
many reasons. Obviously, it is vital to
maintain the hard earned integrity of the
field of dermatology. In addition, the dis-
coveries made though cosmetic derma-
tology research will likely benefit other
fields of dermatology. For example,
research into the anti-aging effects of
antioxidants may lead to enhanced
knowledge of chemopreventive tech-
niques to be used to prevent skin cancer.
Advances in acne therapy, vitiligo and
other disorders of pigmentation are also
possible. In fact, it is interesting to note

that the development of Vaniqa™, a
cream designed to slow hair growth in
women with facial hair, has led to the
availability of an intravenous treatment
for African Sleeping Sickness, a major
cause of death in Africa. Without the
financial incentive to develop Vaniqa,
which is used for purely aesthetic pur-
poses, this life-saving drug would not be
available. For many reasons, all pharma-
ceutical, medical device, and cosmetic
companies should be encouraged to
research their products.
Although there is much research per-
formed by cosmetic companies on the
effects of cosmetics on the skin, much of
this data is proprietary and is not pub-
lished nor shared with the rest of the sci-
entific community. The reasons for this
are numerous, but competition between
companies and the desire to be the first
to come out with a new “miracle prod-
uct” are prominent among them.
However, the issue is even more com-
plex. The FDA has different definitions
for drugs and cosmetics. Cosmetic prod-
ucts do not have to be researched in any
standard way because FDA approval is
not required. Instead, cosmetic products
are voluntarily registered by the compa-

nies that develop them. However, drugs
must undergo years of expensive trials
establishing both safety and efficacy
before receiving FDA approval (see
Ch 28). This disparity means that a com-
pany is more reluctant to publish data
that could cause their product to be
labeled as a drug.
The dearth of published data on cos-
metic products has forced physicians,
aestheticians, and lay people to rely on
sales people and marketing departments
to obtain information about cosmetic
formulations. This has led to much mis-
information that has diminished the
credibility of cosmetic products and the
cosmetic field in general. Because an
ever-increasing number of dermatolo-
gists and other physicians are practicing
“cosmetic dermatology,” it is imperative
that the cosmetic dermatologist practice
evidence-based medicine in order to dis-
tinguish efficacious treatments from
mere marketing hype. This text sifts
through the knowledge of the effects
cosmetic products and procedures have
on the skin and its appearance. The
amount of research that should still be
performed is daunting; however, the
field is young and the rewards are great.

I encourage everyone to join me in the
exciting endeavor to find scientifically
proven methods of improving the
appearance of the skin.
Leslie Baumann, MD
“Don’t worry if your job is small,
And your rewards are few.
Remember that the mighty oak,
Was once a nut like you.”
Anonymous
PREFACE
PREFACE
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xiii
ACKNOWLEDGMENTS
ACKNOWLEDGMENTS
The first edition of this book was
printed in 4 languages and was the best-
selling textbook on cosmetic dermatol-
ogy worldwide (or so I have been told).
There are many people to thank for this
and the many wonderful things that
have occurred in the last 6 years. First I
would like to thank Dr. Stephen Mandy
who took me in as a newly graduated
resident in 1997, and let me and my hus-
band live with him for two weeks while
he taught me about the newly emerging
field of cosmetic dermatology. (I learned
to inject collagen on his secretary!) That

was the beginning of what has now
been an 11-year friendship. Dr. Francisco
Kerdel negotiated my first job and office
space and he and Dr. William Eaglstein
mentor me to this day. They were
thanked in the first edition but I will
never be able to thank them enough for
what they have done for me.
This year, the University of Miami
Miller School of Medicine decided to
create the Cosmetic Medicine and
Research Institute (CMRI), which con-
sists of cosmetic dermatology, oculo-
plastic surgery, facial plastic surgery and
nutrition. The role of this multi-spe-
cialty institute is to provide cutting edge
dermatologic and surgical procedures to
enhance appearance. By combining
accomplished physicians from the vari-
ous cosmetic specialties, the Institute
can offer patients the expertise of many
different types of physicians in order to
achieve the best outcome. The mission
of the Institute is to perform research in
the area of cosmetic medicine, and many
genetic initiatives to look for the genetic
influences on appearance have begun.
In addition, the CMRI will provide
training to physicians on cosmetic der-
matology and cosmetic procedures. (See

www.derm.net for more information.)
I am very proud to announce that I
have been selected to be the Director of
the University of Miami Cosmetic
Medicine and Research Institute. For
this honor I would like to thank several
people for believing in me and giving me
this opportunity:
Pascal Goldschmidt, MD (the Dean of
the University of Miami Medical
School) – Dr. Goldschmidt is a true
visionary and a leader in the field of
the genetic influences in atherosclero-
sis. He opened the doors to basic sci-
ence research for me and shared his
genetic research team with me until I
could find funding. In addition, he did
the great honor of introducing me to
Bart Chernow, MD and William
O’Neil, MD (both of whom are Vice
Deans at the University of Miami).
The three of them appointed me
Director of the University of Miami
Cosmetic Medicine and Research
Institute and gave me one of the most
wonderful opportunities of my life.
Dr. Chernow is a brilliant man and a
true magician because he can pull all
kinds of opportunities and ideas and
innovations “out of his hat.” I con-

sider Bart and his wife Peggy good
friends and I thank them both for
their support.
I would like to thank David Seo, MD,
my partner on the genetic trials, for
his patience in getting me up to speed
on genetic research. My fingers are
crossed that we will discover great
things together in the next 2 years.
Thanks to the doctors who are a part
of the CMRI and have chapters in this
text. They have all taught me so
much and are great to work with:
Drs. Lisa Grunebaum, Joely Kaufman,
Wendy Lee, Heather Woolery-Lloyd,
and Larissa Zaulyanov-Scanlan.
Thanks to Neal Shapiro for handling
the financial aspect of the Institute so
that I can concentrate on my true
loves…seeing patients and perform-
ing research. Huge hugs and thanks to
Susan Schaffer-RN who is my great
friend, confidant, and Head of
Nursing for the CMRI. She travels
around the world with me, lecturing
on cosmetic issues and helping to
keep me sane. Edmund Weisberg-
you are hilarious and fun to work
with. I would never have written the
first edition of this book without you!

Stephanie and Fransheley- you have
worked with me for many years and I
have loved it and I look forward to
MANY more.
I would like to thank Catherine
Drayton and Richard Pine, my book
agents for my NY Times bestselling
book called “The Skin Type Solution”
(Bantam 2005) (www.skintypesolu-
tions.com). They negotiated an
unprecedented book deal for me and
are the best in the field. I first unveiled
the Baumann Skin Typing System in
this book. Catherine- Thanks for all
the attention that you give to me in
spite of the fact that we live on oppo-
site sides of the world (and thanks for
taking me sailing with you in Australia
when I was there for the book launch-
that was SO COOL!). I will never for-
get the support that Irwin Applebaum
and his amazing team at Bantam Dell
(a division of Random House) gave
The Skin Type Solution when it
launched. Phillip Rappaport is a great
editor and friend.
I would like to thank my family, to
whom this book is dedicated. My
husband Roger and my sons Robert
and Max are a constant source of joy

and strength for me. I love cooking
with them! I am fortunate to be very
close with both my mother, Lynn
McClendon, and my mother-in-law,
Josie Kenin. They are great role mod-
els and friends and I am very lucky to
have them. Thanks to my friends Jill
Cooper, Melina Goldstein, Sofie
Matz and Debbie Kramer for listening
to me and keeping me calm.
Dr. Sogol Saghari, who was my fel-
low for one year and now has a der-
matology practice in Los Angeles,
made huge contributions to this
book. She helped on the first draft of
many of the chapters. She is a brilliant
dermatologist and an incredibly nice
person. I was so lucky to have her as a
fellow. Thanks to all the doctors who
contributed to the chapters in this
book. Special thanks to Mohammed
Lotfy, MD, who was available 24
hours a day helping me with litera-
ture searches and drawing the illustra-
tions. He is one of the most dedicated
dermatologists I have ever met. Inja
Bogdan, MD and Maria Paz
Castanedo-Tardan, MD were also fel-
lows that contributed chapters and
have great careers ahead of them.

And last but certainly not least-
I would like to thank Anne Sydor for
convincing me to write the second
edition of this book. I never would
have been able to get up at 5am and
get this done if you had not encour-
aged me. Thanks for being my cheer-
leader and for lighting a fire in me to
get this done . . . FINALLY! I am so
proud of this book and poured my
soul into it. I hope that all of you
enjoy reading it as much as I enjoyed
writing it.
Affectionately,
Leslie Baumann, MD
ACKNOWLEDGMENTS
xiv
1
SECTION
Basic Concepts of Skin
Science
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3
CHAPTER 1 ■ BASIC SCIENCE OF THE EPIDERMIS
CHAPTER 1
Basic Science of the
Epidermis
Leslie Baumann, MD
Sogol Saghari, MD
develop.

1
In other words, an acidic type
and a basic type are always expressed
together and they form a keratin fila-
ment together. Keratinocytes are “born”
at the base of the epidermis at the der-
mal–epidermal junction (DEJ). They are
produced by stem cells, which are also
called basal cells because they reside at
the base, basal layer, of the epidermis.
When the stem cells divide, they create
“daughter cells,” which slowly migrate
to the top of the epidermis. This process
of daughter cells maturing and moving
to the top is called keratinization.
As these cells progress through the
epidermis and mature, they develop dif-
ferent characteristics. The layers of the
epidermis are named for these character-
istic traits. For example, as mentioned,
the first layer is the basal layer because it
is located at the base of the epidermis.
Basal cells are cuboidal in shape. The
next layer is referred to as the spinous
layer because the cells in this layer have
prominent, spiny attachments called
desmosomes. Desmosomes are complex
structures composed of adhesion mole-
cules and other proteins and are integral
in cell adhesion and cell transport. The

next layer is the granular layer, named so
because these cells contain visible kera-
tohyaline granules. The last, outermost
layer is the stratum corneum (SC), a con-
densed mass of cells that have lost their
nuclei and granules (Figs. 1-1 and Fig.
1-2). The SC is covered by a protein
material called the cell envelope, which
aids in providing a barrier to water loss
and absorption of unwanted materials.
As keratinocytes migrate through the
layers of the epidermis, their contents
and functions change according to, or
depending on, the specific epidermal
layer in which they are moving. Although
the functions of the keratinocyte have
not been completely elucidated, many
of them are understood. It is known
that keratinocyte activity, such as the
release of cytokines, can be affected by
topical products administered to the
skin. Keratinocytes and their compo-
nents at each level of the epidermis
starting at the basal layer and proceed-
ing to the superficial layers of the epi-
dermis are described below.
Keratinocyte Function
THE BASAL LAYER (STRATUM BASALE)
Basal cells join with other basal and the
overlying spinous cells via desmosomes,

thus forming the basement membrane.
These basal keratinocytes contain ker-
atins 5 and 14, mutations in which result
in an inherited disease called epidermoly-
sis bullosa simplex. Keratins 5 and 14 are
presumed to establish a cytoskeleton that
permits flexibility of the cells. This flexi-
bility allows cells to proceed out of the
basal layer and migrate superficially, thus
undergoing the keratinization process.
Basal cells are responsible for maintain-
ing the epidermis by continually renewing
the cell population. Of the basal layer,
10% of cells are stem cells, 50% are
amplifying cells, and 40% are postmitotic
cells. Normally, stem cells are slowly
dividing cells, but under certain conditions
such as wound healing or exposure to
growth factors, they divide faster. They
give rise to transient amplifying cells.
Transient amplifying cells are responsible
for most of the cell division in the basal
layer and produce postmitotic cells, which
undergo terminal differentiation and
move superficially to become suprabasal
cells that continue their upward migration
to become granular cells and ultimately
part of the SC (Fig. 1-3).
THE SPINOUS LAYER (STRATUM SPINOSUM)
Keratins 1 and 10 are first seen in this

layer of suprabasal keratinocytes. These
keratins form a more rigid cytoskeleton
The skin is composed of three primary
layers: epidermis, dermis, and subcuta-
neous tissue. Each layer possesses
specific characteristics and functions.
Although research regarding skin layers
continues, much is already known about
the structure of each component. New
discoveries about these components
have already led to prenatal diagnoses
of many inherited diseases and to
improved therapies. In the future, study
of these components will likely lead to
an enhanced understanding of skin
aging and the effects of topical products
on the biologic function of the skin.
The epidermis is the most superficial
layer of the skin. It is very important
from a cosmetic standpoint, because it is
this layer that gives the skin its texture
and moisture, and contributes to skin
color. If the surface of the epidermis is
dry or rough, the skin appears aged.
Knowledge of the basic structure of the
epidermis best enables a practitioner to
improve the appearance of patients’ skin.
THE KERATINOCYTE
Keratinocytes, also known as corneo-
cytes, are the cells that comprise the

majority of the epidermis. Keratin fila-
ments are major components of the
keratinocytes, and provide structural
support. There are two types of keratin
filaments: acidic (type I, K10–20) and
basic (type II, K 1–10). They both must
be expressed for a keratin filament to
į FIGURE 1-1 The layers of the epidermis.
DERMIS
Desquamating cell
Stratum corneum
Granular layer
Spinous layer
Basal layer
Keratohyaline
granule
Desmosome
į FIGURE 1-2 Histopathology of the epidermis
demonstrating the four layers. (Image courtesy of
George Ioannides, MD.)
Keratohyaline
granules
Desmosomes
Stratum
corneum
Granular
layer
Spinous
layer
Basal

layer
Dermis
4
that confers greater mechanical strength
to the cell. It is worth mentioning that
under hyperproliferative conditions such
as actinic keratosis, wound healing, and
psoriasis, keratins 6 and 16 are upregu-
lated in the suprabasal keratinocytes.
Lamellar granules, which are consid-
ered the first sign of keratinization, first
appear in this layer. They contain lipids
such as ceramides, cholesterol, and fatty
acids as well as enzymes such as pro-
teases, acid phosphatase, lipases, and
glycosidases. It has been recently shown
that cathelicidin, an antimicrobial
peptide, is also stored in the lamellar
granules.
2
These granules migrate to the
surface and expel their contents by exo-
cytosis. The released lipids coat the sur-
face, imparting barrier-like properties.
Desmosomes are very prominent in this
layer, thus accounting for the name
“spinous layer.”
The advanced stage of differentiation
of suprabasal keratinocytes is conducive
to staining for products not found on

basal cells (i.e., sugar complexes and
blood group antigens). The cytoplasm
contains proteins not found in the lower
layers such as involucrin, keratolinin,
and loricrin. These proteins become
cross-linked in the SC to confer strength
to the layer.
THE GRANULAR LAYER (STRATUM GRANULO-
SUM) Granular layer keratinocytes reside
in the uppermost viable layer of the epi-
dermis. The “granules” represent kerato-
hyaline granules, which contain profilag-
grin, the precursor to filaggrin. The pro-
tein filaggrin cross-links keratin filaments
providing strength and structure. The pro-
teins of the cornified cell envelope
(involucrin, keratolinin, pancornulins, and
loricrin) are cross-linked in this layer by
the calcium-requiring enzyme transgluta-
minase (TGase) to form the cell envelope.
There are four types of transglutaminases
present in the epidermis: TGase 1 or ker-
atinocyte TGase, TGase 2 or tissue
TGase, TGase 3 or epidermal TGase, and
TGase 5. Only TGases 1, 3, and 5 partici-
pate in the development of the corneo-
cyte envelope (CE) formation. TGase 2
has other functions including a role in
apoptosis (programmed cell death). It is
known that TGase activity increases with

the elevation of Ca
2+
levels in the
medium of cultured keratinocytes.
3
This
in turn results in the formation of the
cornified cell envelope and differentia-
tion of keratinocytes.
4,5
The active
metabolite of vitamin D, known as 1,25-
dihydroxyvitamin D
3
[1,25(OH)
2
D
3
],
also plays a role in keratinocyte differenti-
ation (Box 1-1). It enhances the
Ca
2+
effect on the keratinocytes,
and increases transglutaminase activity as
well as involucrin levels,
6
the combined
effects of which induce CE formation.
7,8

Calcium is known to be an inducer of
differentiation and a suppressor of prolif-
eration in epidermal keratinocytes.
9,10
It
has been shown that in the state of low
Ca
2+
levels (0.05 mM), keratinocytes are in
a proliferative stage, while increases in
Ca
2+
levels (0.10–0.16 mM) lead to expres-
sion of differentiation markers such as ker-
atins 1 and 10, TGase, and filaggrin.
9
Granular cells exhibit anabolic proper-
ties such as synthesis of filaggrin, corni-
fied cell envelope proteins, and high
molecular weight keratins. In addition,
they show catabolic events such as dis-
solution of the nucleus and organelles.
THE HORNY LAYER (SC) The most superfi-
cial layer of the epidermis is the SC or
horny layer, which is, on average,
approximately 15-cell layers thick.
13,14
The keratinocytes that reside in this
layer are the most mature and have com-
pleted the keratinization process. These

keratinocytes contain no organelles and
their arrangement resembles a brick
wall. The SC is composed of protein-rich
corneocytes embedded in a bilayer lipid
matrix assembled in a “brick and mortar”
fashion. The “bricks” are composed of
keratinocytes and the “mortar” is made
up of the contents extruded from the
lamellar granules including lipids and
proteins (Fig. 1-4). Cells of the midcorni-
fied layer have the most amino acid con-
tent and therefore have the highest capa-
bility for binding to water, while the
COSMETIC DERMATOLOGY: PRINCIPLES AND PRACTICE
BOX 1-1
1,25-Dihydroxyvitamin D
3
[1,25(OH)
2
D
3
] stimulates differentiation and prohibits proliferation of
the keratinocytes. It exerts its effects via the nuclear hormone receptor known as vitamin D
receptor (VDR). VDR operates with the aid of coactivator complexes. There are two known coacti-
vator complexes: vitamin D interacting protein complex (DRIP) and the p160 steroid receptor
coactivator family (SRC/p160). It has been proposed that the DRIP mediator complex is involved
in proliferation and early differentiation while the SRC/p160 complex is engaged in advanced dif-
ferentiation.
11
The vitamin D receptors of undifferentiated keratinocytes bind to the DRIP com-

plex, inducing early differentiation markers of K1 and K10.
12
The DRIP complex on the vitamin D
receptor is then replaced by the SRC complex. The SRC complex induces gene transcription for
advanced differentiation, which occurs with filaggrin and loricrin.
12
The replacement of the DRIP
complex with the SRC complex on the vitamin D receptor is believed to be necessary for ker-
atinocyte differentiation. It is important to realize that vitamin D levels are lower in older people
and that this reduction may play a role in the slower wound healing characteristic in the elderly.
į FIGURE 1-3 The stem cells divide and produce amplifying cells that greatly increase the number of
keratinocytes. These in turn become the mature, terminal, and differentiated cells. The numbers indicate
the cell generation.
3
3
2
4
4
4
4
5
5
5
5
5
5
5
5
6
6

6
6
6
6
6
6
1
Stem Cells
Transit
amplifyin
g
Terminally
differentiated
5
deeper layers have less water-binding
capacity.
15
The SC is described as the
“dead layer” of cells because these cells
do not exhibit protein synthesis and are
unresponsive to cellular signaling.
16
The horny layer functions as a protec-
tive barrier. One of its protective func-
tions is to prevent transepidermal water
loss (TEWL). Amino acids and their
metabolites, which are by-products
formed from the breakdown of filaggrin,
comprise a substance known as the
natural moisturizing factor (NMF).

Intracellularly-located NMF and lipids
released by the lamellar granules,
located extracellularly, play an impor-
tant role in skin hydration, suppleness,
and flexibility (see Chapter 11).
The Cell Cycle
The above keratinization process is also
referred to as the “cell cycle.” The normal
cell cycle of the epidermis is from 26 to 42
days.
17
This series of events, known also
as desquamation, normally occurs invisi-
bly with shedding of individual cells or
small clumps of cells. Disturbances of this
process may result in the accumulation of
partially detached keratinocytes, which
cause the clinical findings of dry skin.
Disease states may also alter the cell
cycle. For example, psoriasis causes a dra-
matic shortening of the cell cycle, result-
ing in the formation of crusty cutaneous
eruptions. The cell cycle lengthens in time
as humans age.
18
This means that the
cells at the superficial layer of the SC are
older and their function may be impaired.
Results from such compromised function-
ing include slower wound healing and a

skin appearance that is dull and lifeless.
Many cosmetic products such as retinol
and alpha hydroxy acids are believed to
quicken the pace of the cell cycle, yielding
younger keratinocytes at the superficial
layers of the SC, thus imparting a more
youthful appearance to the skin.
GROWTH FACTORS
Growth factors can be classified into
two groups: proliferative and differen-
tiative factors. Proliferative factors
engender more DNA synthesis and
result in proliferation of the cells.
Differentiative factors inhibit the pro-
duction of DNA and suppress growth,
thereby resulting in differentiation of
the keratinocytes. Epidermal growth
factor (EGF) is one of the integral
chemokines in the regulation of growth
in human cells. It binds to the epidermal
growth factor receptor (EGFR) located
on the basal and suprabasal cells in the
epidermis and activates tyrosine kinase
activity, which ultimately results in pro-
liferation of the cells.
19
Keratinocyte
growth factor (KGF), a member of the
fibroblast growth factor family, also has
a proliferative effect via the tyrosine

kinase receptor on epidermal cells.
20
It
has been shown that KGF contributes to
and enhances wound healing.
21
In addi-
tion, KGF has been demonstrated
to enhance hyaluronan synthesis in
the keratinocytes.
22
Other important
growth factors include the polypeptide
transforming growth factors, which
consist of two types: Transforming
growth factor alpha (TGF-␣) and trans-
forming growth factor beta (TGF-␤).
They differ in both configuration and
function. TGF-␣ is a proliferative factor,
similar to EGF, and works by stimulating
a tyrosine kinase response. TGF-␤,
which includes three subtypes (1–3), is
a differentiative factor with a serine/
threonine kinase receptor. TGF-␤1 and
TGF-␤2 are present in small amounts in
the keratinocytes. The presence of
calcium, phorbol esters, as well as
TGF-␤ itself increases the epidermal
TGF-␤ level and promotes differentia-
tion.

23
TGF-␤ has also been proven to
have a role in scarring, and antibodies to
this factor have been shown to decrease
the inflammatory response in wounds
and reduce scarring.
24, 25
ANTIMICROBIAL PEPTIDES
Antimicrobial peptides (AMPs) have
recently become an area of interest
because of their involvement in the innate
immune system of human skin. AMPs
exhibit broad-spectrum activity against
bacteria, viruses, and fungi.
26,27
The
cationic peptide of the AMPs attracts the
negatively charged bacteria, becoming
pervasive in the bacterial membrane in
the process, and ultimately eliminates the
bacteria. Cathelicidin and defensin are the
two major groups of AMPs believed to
have an influence in the antimicrobial
defense of the skin. Cathelicidin has been
identified in the keratinocytes of human
skin at the area of inflammation, as well
as in eccrine and salivary glands.
28–30
In
addition to antimicrobial activity, catheli-

cidin LL-37 demonstrates a stimulatory
effect on keratinocyte proliferation in the
process of wound healing.
31
Pig catheli-
cidin PR-39 has been shown to induce
proteoglycans production (specifically,
syndecan-1 and -4) in the extracellular
matrix in wound repair.
32
Defensin is also
expressed in the human keratinocytes
33
and mucous membranes.
34,35
␤-Defensin
1 seems to promote differentiation in the
keratinocytes by increasing expression of
keratin 10.
36
Interestingly, UVB radiation
has been shown to increase the levels of
human ␤-defensin mRNA in the ker-
atinocytes.
37
AMPs have been demonstrated to be
involved in several dermatologic condi-
tions including atopic dermatitis, psoria-
sis, and leprosy,
27

as well as wound heal-
ing, all of which are beyond the scope of
our discussion. The role of AMPs in the
epidermal barrier will be discussed in
Chapter 11.
MOISTURIZATION OF THE SC
The main function of the SC is to
prevent TEWL and regulate the water
balance in the skin. The two major com-
ponents that allow the SC to perform
this role are lipids and the NMF.
CHAPTER 1 ■ BASIC SCIENCE OF THE EPIDERMIS
KeratinocytesDesmosomesIntercellular
lipids(fats)
į FIGURE 1-4 The desmosomes form attachments between the keratinocytes. The keratinocytes are
surrounded by lipids. These structures form the skin barrier.
6
Natural Moisturizing Factor
Released by the lamellar granules, NMF
is composed of amino acids and their
metabolites, which are by-products
formed from the breakdown of filaggrin
(Box 1-2). NMF is found exclusively
inside the cells of the SC and gives the
SC its humectant (water-binding) quali-
ties (Fig. 1-5). NMF is composed of very
water-soluble chemicals; therefore, it
can absorb large amounts of water, even
when humidity levels are low. This
allows the SC to retain a high water con-

tent even in a dry environment. The
NMF also provides an important aque-
ous environment for enzymes that
require such conditions to function. The
importance of NMF is clear when one
notes that ichthyosis vulgaris patients,
who have been shown to lack NMF,
manifest severe dryness, and scaling of
the skin.
38
It has been demonstrated that
normal skin exposed to normal soap
washing has significantly lower levels of
NMF when compared to normal skin
not washed with surfactants.
39
NMF lev-
els have also been reported to decline
with age, which may contribute to the
increased incidence of dry skin in the
elderly population (see Chapter 11).
Lipids
In order of abundance, the composition
of skin surface lipids includes triglyc-
erides, fatty acids, squalene, wax esters,
diglycerides, cholesterol esters, and cho-
lesterol.
41
These lipids are an integral part
of the epidermis and are involved in pre-

venting TEWL and the entry of harmful
bacteria. They also help prevent the skin
from absorbing water-soluble agents. For
decades it has been known that the
absence of lipids in the diet leads to
unhealthy skin (see Chapter 11). More
recently, it has been shown that inherited
defects in lipid metabolism, such as the
deficiency of steroid sulfatase seen in X-
linked ichthyosis, will lead to abnormal
skin keratinization and hydration.
42
It is
now known that SC lipids are affected by
age, genetics, seasonal variation, and diet.
Deficiency of these lipids predisposes the
individual to dry skin. This has been
demonstrated in mice with essential fatty
acid deficiency (EFAD); when fed a diet
deficient in linoleic acid these mice devel-
oped increased TEWL.
43
Interestingly,
administration of hypocholesterolemic
drugs has also been associated with dry
skin changes.
44
Skin lipids are produced in and
extruded from lamellar granules as
described above or are synthesized in

the sebaceous glands and then excreted
to the skin’s surface through the hair
follicle. The excretion of sebum by seba-
ceous glands is hormonally controlled
(see Chapter 10). Lipids help keep the
NMF inside the cells where it is needed
to keep cells hydrated and aqueous
enzymes functioning. Although this is
less well characterized, lipids can them-
selves influence enzyme function.
ROLE OF LIPIDS IN TEWL
The major lipids found in the SC that con-
tribute to the water permeability barrier
are ceramides, cholesterol, and fatty acids.
Since the 1940s, when the SC was
first identified as the primary barrier to
water loss, many hypotheses have been
entertained as to exactly which lipids
are important in the SC. The research
with the EFAD mice described above led
to a focus on phospholipids because
they contain linoleic acid. However, it
was later found that phospholipids are
almost completely absent from the SC.
40
In 1982, ceramide 1 was discovered.
This lipid compound is rich in linoleic
acid and is believed to play a major role
in structuring SC lipids essential for bar-
rier function.

45
Later, five more distinct
types of ceramides were discovered and
named according to the polarity of the
molecule. Ceramide 1 is the most non-
polar and ceramide 6 is the most polar.
Although the ceramides were once
thought to be the key to skin moisturiza-
tion, studies now suggest that no particu-
lar lipid is more important than the oth-
ers. It appears that the proportion of fatty
acids, ceramides, and cholesterol is the
most important parameter. This was
demonstrated in a study in which after
altering the water barrier with acetone,
the application of a combination of
ceramides, fatty acids, and cholesterol
resulted in normal barrier recovery.
46
Application of each of the separate enti-
ties alone resulted in delayed barrier
recovery. Manufacturers now include
ceramides or a mixture of ceramides, cho-
lesterol, and fatty acids in several avail-
able products as a result of these findings.
However, the use of these mixtures to
COSMETIC DERMATOLOGY: PRINCIPLES AND PRACTICE
BOX 1-2
Filaggrin, named for filament aggregating
protein, derived its name from the fact that it

binds keratin filaments to form a structural
matrix in the SC. Genetic defects in the filag-
grin gene are known to play a role in a sub-
set of ichthyosis vulgaris cases.
38
Interestingly, filaggrin is not present in the
superficial layers of the SC. Studies have
shown that it is completely degraded into
amino acids within 2 to 3 days of profilaggrin
formation and its constituents are further
metabolized to form the NMF.
40
This is
nature’s way of keeping its water-binding
capabilities in the top layer of the SC where
they are needed while preventing the lower
layers of the SC from being disrupted by
having too much water present. In addition,
the level of NMF is regulated by the water
activity present in the SC.
į FIGURE 1-5 The keratinocytes are embedded in a lipid matrix that resembles bricks and mortar.
Natural moisturizing factor (NMF) is present within the keratinocytes. NMF and the lipid bilayer prevent
dehydration of the epidermis.
DEEP
SUPERFICIAL
NMF
Brick
Mortar
Brick
Hydrophilic

Hydrophilic
Hydrophobic
Corneocytes (bricks)
Intercellular lipids
(mortar)
7
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Syndecans, cell surface heparan sulfate
proteoglycans, are induced by a proline-
rich antimicrobial peptide from wounds.
Proc Natl Acad Sci U S A. 1994;91:11035.
33. Ali RS, Falconer A, Ikram M, et al.
Expression of the peptide antibiotics
human beta defensin-1 and human beta
defensin-2 in normal human skin. J Invest

Dermatol. 2001;117:106.
34. Mathews M, Jia HP, Guthmiller JM, et al.
Production of beta-defensin antimicro-
bial peptides by the oral mucosa and sali-
vary glands. Infect Immun. 1999;67:2740.
35. Dunsche A, Acil Y, Dommisch H, et al.
The novel human beta-defensin-3 is
widely expressed in oral tissues. Eur J
Oral Sci. 2002;1110:121.
36. Frye M, Bargon J, Gropp R. Expression of
human beta-defensin-1 promotes differ-
entiation of keratinocytes. J Mol Med.
2001;79:275.
37. Seo SJ, Ahn SW, Hong CK, et al. Expressions
of beta-defensins in human keratinocyte cell
lines. J Dermatol Sci. 2001;27:183.
38. Sybert VP, Dale BA, Holbrook KA.
Ichthyosis vulgaris: identification of a
defect in synthesis of filaggrin correlated
with an absence of keratohyaline gran-
ules. J Invest Dermatol. 1985;84:191.
39. Scott IR, Harding CR. Physiological
effects of occlusion-filaggrin retention
(abstr). Dermatology. 1993;2000:773.
40. Rawlings AV, Scott IR, Harding CR, et al.
Stratum corneum moisturization at the
molecular level. J Invest Dermatol. 1994;
103:731.
41. Downing DT, Strauss JS, Pochi PE.
Variability in the chemical composition

of human skin surface lipids. J Invest
Dermatol. 1969;53:322.
42. Webster D, France JT, Shapiro LJ, et al. X-
linked ichthyosis due to steroid-sul-
phatase deficiency. Lancet. 1978;1:70.
43. Prottey C. Essential fatty acids and the
skin. Br J Dermatol. 1976;94:579.
44. Elias PM. Epidermal lipids, barrier func-
tion, and desquamation. J Invest Dermatol.
1983;80:44s.
45. Swartzendruber DC, Wertz PW, Kitko DJ,
et al. Molecular models of the intercellular
lipid lamellae in mammalian stratum
corneum. J Invest Dermatol. 1989;92:251.
46. Man MQ, Feingold KR, Elias PM.
Exogenous lipids influence permeability
barrier recovery in acetone-treated
murine skin. Arch Dermatol. 1993;129:728.
CHAPTER 1 ■ BASIC SCIENCE OF THE EPIDERMIS
treat atopic dermatitis and other ichthy-
otic disorders has been disappointing.
SUMMARY
The epidermis is implicated in many of
the skin complaints of cosmetic patients.
It is the state of the epidermis that
causes the skin to feel rough and appear
dull. A flexible, well-hydrated epidermis
is more supple and radiant than a dehy-
drated epidermis. The popularity of buff
puffs, exfoliating scrubs, masks, mois-

turizers, chemical peels, and microder-
mabrasion attest to the obsession that
cosmetic patients have with the condi-
tion of their epidermis. It is important to
understand the properties of the epider-
mis in order to understand which cos-
metic products and procedures can truly
benefit patients as opposed to those that
are based on myths or hype.
REFERENCES
1. Chu D. Overview of biology, develop-
ment, and structure of skin. In: Wolff K,
Goldsmith L, Katz S, Gilchest B, Paller A,
Leffell D, eds. Fitzpatrick’s Dermatology in
General Medicine. 7th ed. New York, NY:
Mcgraw-Hill; 2008:60.
2. Braff MH, Di Nardo A, Gallo RL.
Keratinocytes store the antimicrobial
peptide cathelicidin in lamellar bodies.
J Invest Dermatol. 2005;124:394.
3. Li L, Tucker RW, Hennings H, et al.
Inhibitors of the intracellular Ca(
2+
)-
ATPase in cultured mouse keratinocytes
reveal components of terminal differenti-
ation that are regulated by distinct intra-
cellular Ca
2+
compartments. Cell Growth

Differ. 1995;6:1171.
4. Green H. The keratinocyte as differenti-
ated cell type. Harvey Lect. 1980;74:101.
5. Eckert RL, Crish JF, Robinson NA. The epi-
dermal keratinocyte as a model for the
study of gene regulation and cell
differentiation. Physiol Rev. 1997;77:397-424.
6. Su MJ, Bikle DD, Mancianti ML, et al.
1,25-Dihydroxyvitamin D
3
potentiates
the keratinocyte response to calcium.
J Biol Chem. 1994;269:14723.
7. Hosomi J, Hosoi J, Abe E, et al.
Regulation of terminal differentiation of
cultured mouse epidermal cells by
1 alpha, 25-dihydroxyvitamin D
3
. Endo-
crinology. 1983;113:1950.
8. Smith EL, Walworth NC, Holick MF.
Effect of 1 alpha,25-dihydroxyvitamin
D
3
on the morphologic and biochemical
differentiation of cultured human epider-
mal keratinocytes grown in serum-free
conditions. J Invest Dermatol. 1986;86:709.
9. Yuspa SH, Kilkenny AE, Steinert PM,
et al. Expression of murine epidermal dif-

ferentiation markers is tightly regulated
by restricted extracellular calcium concen-
trations in vitro. J Cell Biol. 1989;109:1207.
10. Sharpe GR, Gillespie JI, Greenwell JR. An
increase in intracellular free calcium is an
early event during differentiation of cul-
COSMETIC DERMATOLOGY: PRINCIPLES AND PRACTICE
8
CHAPTER 2
Basic Science of
the Dermis
Leslie Baumann, MD
Sogol Saghari, MD
is known about the attachment proteins
found in the basement membrane of the
DEJ. At this point there are no known
cosmetic implications for this area, as
such a discussion is beyond the scope of
this book. Instead, this chapter will
focus on the components of the dermis
that are known to be important in aging.
COLLAGEN
Collagen, one of the strongest natural
proteins and the most abundant one in
humans as well as in skin, imparts dura-
bility and resilience to the skin. It has
been the focus of much antiaging
research and the target of several skin
products and procedures. The impor-
tance of collagen is emphasized in the

literature regarding many of the topical
agents that are touted to increase colla-
gen synthesis such as glycolic and ascor-
bic acids. Resurfacing techniques such as
the CO
2
laser and dermabrasion are
intended to change collagen structure,
thereby improving skin texture. Various
forms of collagen are injected into the
dermis to replace damaged collagen and
to reverse the signs of aging. Finally, top-
ical retinoids have been shown to
reduce the collagen damage that occurs
because of sun exposure. These sundry
aspects of collagen health or replace-
ment will be discussed separately in
upcoming chapters; however, it is neces-
sary first to gain an understanding of the
structure and function of collagen.
“Collagen” is actually a complex
family of 18 proteins, 11 of which are
present in the dermis. Collagen fibers
are always seen in the dermis in the
final, mature state of assembly as
opposed to elastin, the immature fibers
of which are seen in the superficial der-
mis with the more mature fibers found
in the deeper layer of the dermis. Each
type of collagen is composed of three

chains (Fig. 2-2). Collagen is synthe-
sized in the fibroblasts in a precursor
form called procollagen. Proline residues
on the procollagen chain are converted
to hydroxyproline by the enzyme pro-
lyl hydroxylase. This reaction requires
the presence of Fe
++
, ascorbic acid (vit-
amin C), and ␣-ketoglutarate. Lysine
residues on the procollagen chain are
also converted to hydroxylysine; in
this case, by the enzyme lysyl hydrox-
ylase. This reaction also requires the
presence of Fe
++
, ascorbic acid, and
␣-ketoglutarate. It is interesting to note
that a deficiency of vitamin C, which is
an essential mediating component in
these reactions, leads to scurvy, a dis-
ease characterized by decreased colla-
gen production.
Collagen Glycation
Glycation of extracellular matrix (ECM)
collagen and proteins plays an impor-
tant role in the aging process. This is
not to be confused with glycosylation
of collagen, which is an enzyme-medi-
ated process in the intracellular step of

collagen biosynthesis. Glycation is a
nonenzymatic series of biologic events
that involves adding a reducing sugar
molecule (such as glucose or fructose)
to ECM collagen and proteins. This
reaction is also known as the Maillard
reaction. The sugar molecule mainly
reacts with the amino group side chains
The dermis lies between the epidermis
and the subcutaneous fat. It is responsible
for the thickness of the skin, and as a
result plays a key role in the cosmetic
appearance of the skin. The thickness of
the dermis varies over different parts of
the body and the size doubles between
the ages of 3 and 7 years and again at
puberty. With aging, this basic layer
decreases in thickness and moisture. The
dermis, which is laden with nerves, blood
vessels, and sweat glands, consists mostly
of collagen. The uppermost portion of
this layer, which lies beneath the epider-
mis, is known as the papillary dermis and
the lower portion is known as the reticu-
lar dermis. Smaller collagen bundles,
greater cellularity, and a higher density in
its vascular elements characterize the
papillary dermis as compared to the retic-
ular dermis. Fibroblasts are the primary
cell type in the dermis. They produce

collagen, elastin, other matrix proteins,
and enzymes such as collagenase and
stromelysin. These structural compo-
nents will be discussed individually
because each exhibits significant charac-
teristics that influence the function of the
skin. Immune cells such as mast cells,
polymorphonuclear leukocytes, lympho-
cytes, and macrophages are also present
in the dermis.
The junction between the epidermis
and dermis is known as the dermal–
epidermal junction (DEJ) (Fig. 2-1). Much
į FIGURE 2-1 Histopathology of the dermal-epidermal junction. The basement membrane separates
the epidermis and the dermis. (Image courtesy of George Loannides, MD.)
Basement membrane
Blood vessel
Epidermis
Dermis
į FIGURE 2-2 Collagen is formed when three chains come together to form a triple helix.
α
2

α
1
α
1
9
CHAPTER 2 ■ BASIC SCIENCE OF THE DERMIS
of lysine and arginine of collagen and

ECM proteins. Subsequently, the prod-
uct of this process undergoes oxidative
reactions resulting in the formation of
advanced glycation end products
(AGEs) (Fig. 2-3). AGEs have been
implicated in the aging process and age-
related diseases such as diabetes melli-
tus,
1–3
chronic renal failure,
4,5
and
Alzheimer’s disease.
6–8
It is believed
that with time, AGEs increase,
9
accu-
mulate on human collagen
10
and elastin
fibers,
11
and contribute to aging of the
skin. As a result of glycation, collagen
networks lose their ability to contract,
and they become stiffer and resistant to
remodeling. Fibroblasts are key ele-
ments for collagen contracture, as they
apply contracture force on the collagen

lattice via their actin cytoskeleton.
12
Glycated collagen modifies the actin
cytoskeleton of the fibroblasts thereby
diminishing their collagen contraction
capacity.
13
Fibroblasts also secrete col-
lagenase (MMP-1), which is essential
for collagen turnover. Glycated collagen
has been proven to decrease levels
of collagenase I (MMP-1), leading to
less tissue remodeling.
14
Studies have
shown that UV exposure may also con-
tribute to the production and function
of AGEs. N
e
⑀-(carboxymethyl) lysine
(CML) is one of the AGEs in which the
amino side chain of lysine is reduced.
This product was shown to accumulate
on elastin tissue of photoaged skin and
proven to be higher in sun-exposed
skin as compared to sun-protected
skin.
11
In addition, it has been proposed
that AGE-modified proteins act as

endogenous photosensitizers in human
skin via oxidative stress mechanisms
induced by UVA light.
15
The Key Types of Collagen Found in
the Dermis (Table 2-1)
Type I collagen comprises 80% to 85%
of the dermal matrix and is responsible
for the tensile strength of the dermis.
The amount of collagen I has been
shown to be lower in photoaged skin,
and to be increased after dermabrasion
procedures.
16
Therefore, it is likely that
collagen I is the most important colla-
gen type in regard to skin aging. Type III
is the second most important form of
collagen in the dermis, making up any-
where from 10% to 15% of the
matrix.
17
This collagen type has a
smaller diameter than type I and forms
smaller bundles allowing for skin plia-
bility. Type III, also known as “fetal col-
lagen” because it predominates in
embryonic life, is seen in higher
amounts around the blood vessels and
beneath the epidermis.

The other types of collagen that are
noteworthy for a cosmetic dermatolo-
gist are type IV collagen, which forms a
structure lattice that is found in the base-
ment membrane zone and type V colla-
gen, which is diffusely distributed
throughout the dermis and comprises
roughly 4% to 5% of the matrix. Type
VII collagen makes up the anchoring fib-
rils in the DEJ. Type XVII collagen is
located in the hemidesmosome and
plays an important structural role as
well. The importance of these collagens
and other structural proteins is evident
in genetic diseases characterized by a
lack of these structures and in acquired
diseases characterized by antibody for-
mation to these important structures.
For example, patients with an inherited
blistering disease known as dominant
dystrophic epidermolysis have been
shown to have a scarcity of type VII col-
lagen with resulting abnormalities in
their anchoring fibrils. An acquired bul-
lous disease, epidermolysis bullosa
acquisita (EBA), is caused by antibodies
to this same collagen type VII. Although
the discussion of these diseases is
beyond the scope of this text, it is inter-
esting that patients with chronic sun

exposure have also been found to have
alterations in collagen type VII. This
may contribute to the skin fragility seen
in elderly patients. Some investigators
have postulated that a weakened bond
between the dermis and epidermis
caused by loss of the anchoring fibrils
(collagen VII) may lead to wrinkle for-
mation.
18
The importance of collagen
and changes seen in aged skin will be
discussed further in Chapter 6.
ELASTIN
Elastic fibers represent one of the essential
components of the ECM of connective
tissue (Fig. 2-4). They confer resilience
į FIGURE 2-3 Glycation of proteins is thought to play a role in the aging process.
Amino group of protein + Sugar → N-substituted glycosylamine + water
Ketosamines
Oxidation
Amadori re-arrangement
Advanced Glycation End Products (AGEs)
TABLE 2-1
Major Collagen Types Found in the Dermis
C
OLLAGEN TYPE OTHER NAME LOCATION FUNCTION % OF DERMIS ASSOCIATED DISEASES
I Bone, tendon, skin Gives tensile strength 80
III Fetal collagen Dermis, GI, vessels Gives compliance 15
IV Basement membranes Forms a lattice

V Dermis, diffusely distributed Unknown 4–5 epidermolysis bullosa
VII Anchoring fibrils Stabilizes DEJ acquisita (EBA), dystrophic
XVII BPAG2, BP 180 Hemidesmosome ? epidermolysis bullosa (EB),
bullous pemphigoid (BP),
herpes gestationis
COSMETIC DERMATOLOGY: PRINCIPLES AND PRACTICE
10
and elasticity to skin as well as other
organs such as the lungs and blood ves-
sels. Elastogenesis starts during fetal life
and reaches its maximum near birth and
the early neonatal period. It then
decreases significantly and is virtually
nonexistent by adult life. Elastic fibers
have two components. Their main com-
ponent is elastin, an amorphous, insolu-
ble connective tissue protein. Elastin is
surrounded by microfibrils, the second
component. Elastin constitutes 2% to
3% of the dry weight of skin, 3% to 7%
of lung, 28% to 32% of major blood
vessels, and 50% of elastic ligaments.
19
Elastin is produced from its precursor
tropoelastin in the fibroblasts as well as
endothelial cells and vascular smooth
muscle cells. In contrast to collagen
fibers, elastin fibers are present in the
dermis in various levels of maturity. The
least mature fibers are called oxytalan.

They course perpendicularly from the
DEJ to the top of the reticular dermis.
More mature elastin fibers, called
elaunin, then attach to a horizontal
plexus of fibers found in the reticular
dermis. Elaunin is more mature because
it has more elastin deposited on the fib-
rillin mesh. The most mature elastin
fibers are unnamed and are found
deeper in the reticular dermis (Fig. 2-5).
Microfibrils play a very important
role in elastogenesis and act as a scaffold
for tropoelastin deposition and assem-
bly.
20
Microfibrils are primarily com-
posed of glycoproteins from the fibrillin
family and microfibril-associated glyco-
protein (MAGP)-1 and -2. Fibrillin-1 has
been shown to be important in elastic
fiber development
21
and wound repair.
22
Microfibrils are adjacent to tropoelastin-
producing cells and parallel to the devel-
oping elastin fiber.
23
The microfibrils
form a template on which tropoelastin is

deposited. The tropoelastin polypep-
tides are then covalently cross-linked to
form elastin. Tropoelastin polypeptides
contain alternating hydrophilic and
hydrophobic regions. The hydrophobic
domains, which are rich in proline,
valine, and glycine, are believed to be
responsible for the elasticity of the
elastin tissue.
24
The hydrophilic
domains on the other hand are rich in
alanine and lysine, and interact with the
enzyme lysyl oxidase in the process of
cross-linking.
25
The cross-linking of
elastin is a complex process necessary
for its proper function and stability. This
process is mediated via the copper-
requiring enzyme lysyl oxidase,
26
and
the subsequent formation of desmosine
and isodesmosine cross-links, which
result in an insoluble elastin network.
27
Elastin is fascinating and although
much is known about it, its relevance in
cosmetic dermatology is unclear. It

seems certain that collagen, hyaluronic
acid (HA), and elastin bind each other
covalently and make up a three-dimen-
sional structure that is impaired in aged
skin. There is a commonly held belief
that these three components must be
increased in order to give skin a younger
appearance. However, the trick is that
de novo elastin production does not
occur in adulthood. Trying to increase
production of elastin in adults will
surely be a focus of cosmetic dermatol-
ogy research in the future.
The elastic fiber’s structure provides
clues about its ability to interact with
HA and collagen. Mature elastic fibers
contain an array of proteoglycans.
Versican is one of the most widely stud-
ied proteoglycans
28
and is a member of
the hyaluronan binding family that also
includes aggrecan and neurocan.
Versican contributes to cell adhesion,
proliferation, and migration and can
interact with multiple ECM proteins to
mediate assembly. Mature elastic fibers
are found at the periphery of collagen
bundles, offering a clue that elastin has
important interactions with collagen as

well as with HA.
Elastic fibers are degraded by the elas-
tolytic enzymes such as human leukocyte
elastase (HLE). With significant levels of
sun exposure, elastin degrades and is seen
as an amorphous substance in the dermis
when viewed by light microscopy. This
resultant “elastosis” is a hallmark of pho-
toaged skin. Interestingly, there are protec-
tive mechanisms in the skin preventing
elastin degradation. Lysozymes are
believed to play a protective role in this
matter. They have been shown to increase
and deposit on the elastin fibers of UV-
exposed skin.
29
By binding to the elastin,
the lysozymes prevent the proper interac-
tion between elastase and elastin,
30
thereby
inhibiting the proteolytic activity of the
elastolytic enzymes.
30,31
It is also believed
that damage to the elastin fibers leads to
the decreased skin elasticity seen in aged
skin.
32
Defects or damage to elastin may

lead to wrinkles even in the absence of
sun exposure and aging. Indeed, in one
case, a child with “wrinkled skin syn-
drome” was shown to have a deficiency
of elastin fibers,
33
which demonstrates
the importance of elastin in skin integrity.
Defective elastic fibers can give rise to
multiple dermatologic diseases including
cutis laxa, pseudoxanthoma elasticum
į FIGURE 2-5 The elastic fiber network in the dermis consists of immature oxytalan fibers in the
superficial dermis and the more mature elaunin fibers in the middle dermis. The most mature elastic
fibers are unnamed and are found in the deep reticular dermis.
į FIGURE 2-4 A and B. Scanning electron micrographs of the elastic fibers in human skin.Adapted from
Fitzpatrick’s Dermatology in General Medicine, seventh edition (McGraw Hill), page 532, with permission.
Deep reticular dermis
Reticular dermis
Elaunin fibers
Papillary dermis
Oxytalan fibers
EPIDERMIS
DE Junction
B
A